1. Field of the Invention
The present invention relates generally to dental prostheses and more particularly to a laboratory analog into which a pin of a dental prosthesis system can be screwed so that it can be worked by a dental surgeon or a prosthesis laboratory technician to adapt its shape to that of a crown or bridge that it is to receive.
The invention also relates to a dental system comprising an analog and a pin screw or a threaded part of a pin specifically adapted to cooperate with the analog.
2. Description of the Prior Art
Prior art analogs are made in one piece comprising a generally circularly cylindrical body incorporating a bore open at an upper end for inserting a pin screw or a threaded part of a pin. To this end, the bore is provided near its opening with a thread adapted to cooperate with the thread of the pin screw or the threaded part of the pin. The bore is closed at its other end.
This type of prior art analog has an upper end reproducing the shape of an upper connecting part of an implant implanted in the jawbone of a patient.
To use the analog to support a pin which is intended to be worked in the laboratory, it must be fixed in laboratory plaster in such a position that its upper end is identically oriented to the upper connecting part of the implant in the mouth. This is necessary for the pin to be worked in an angular position or an orientation identical to that which it will have when it is fixed to the implant implanted in the mouth.
This operation of angularly positioning or orienting the upper end of the analog is effected by means of a part referred to as the xe2x80x9ctransferxe2x80x9d. The transfer is placed on the implanted implant and fixed by a clamping screw clamped into the implant so that it has a particular angular position. That angular position is fixed by means of an implant paste or other material known in the art, trapping said clamped screw and the associated transfer. The combination consisting of the clamping screw and the transfer fastened to each other is then unscrewed from the implant and screwed again into the analog in order to fix the angular position of its upper end while fixing it in the laboratory plaster or other material known in the art.
When the analog has been fixed in laboratory plaster, the pin is screwed onto it as far as the stop on the pin screw or the threaded stud carried by said pin and is milled.
Milling the pin causes vibrations that are transmitted to the pin screw or to the threaded stud of the pin, which can cause said pin to become unscrewed while it is being worked.
To remedy this drawback, the present invention proposes a laboratory analog adapted to have a pin of a dental prosthesis system screwed into it so that it can be worked, the analog having at least two parts threaded one inside the other, including an upper part, having an upper end reproducing a connecting upper part of an implant implanted in the jawbone of a patient, and a lower part, one of the two parts accommodating a thread for screwing in the pin and the other part including rotation-preventing means adapted to cooperate through complementary shapes with a pin screw or a threaded part of the pin screwed into the thread to prevent it rotating.
In accordance with the invention, the rotation-preventing means advantageously cooperate male-female-fashion with one end of the pin screw or the threaded part of the pin.
In a preferred embodiment of the analog in accordance with the invention the thread is in the upper part and the rotation-preventing means are at an upper end of the lower part.
In this preferred embodiment the rotation-preventing means include a housing adapted to receive one end of the pin screw or the threaded part of the pin. They can equally include an axial projection adapted to engage in a housing of complementary shape at one end of the pin screw or the threaded part of the pin.
This preferred embodiment of the analog in accordance with the invention also includes an intermediate part adapted to be placed between the upper and lower parts, having at its upper end a thread for the pin to screw into, and adapted to assume different angular positions about an axis of the analog relative to the upper part before it is fixed in laboratory plaster.
Because of the intermediate part, the head of the pin screw can therefore be positioned on the analog in an angular position identical to that which it has on the implant. This is particularly advantageous when the head of the pin screw is designed to project from the gum of the patient and form with the pin, to whose shape its shape is complementary, a single volume intended to receive the crown or the bridge and therefore to be worked in the laboratory, just like the pin.
An outside surface of the intermediate part advantageously carries means for immobilizing it against movement in axial translation and in rotation when it is fixed in laboratory plaster. The immobilizing means can include fins regularly distributed over the perimeter of the outside surface.
In one embodiment of the analog in accordance with the invention the thread is at an upper end of the lower part and the rotation-preventing means are in the upper part.
In this case the analog advantageously also includes an intermediate part adapted to be placed between the upper and lower parts, having the rotation-preventing means at its upper end, and adapted to assume different angular positions about an axis of the analog relative to the upper part before it is fixed in laboratory plaster.
An outside surface of the intermediate part advantageously also carries means for immobilizing it against movement in axial translation and in rotation when it is fixed in laboratory plaster. The immobilizing means can include fins regularly distributed over the perimeter of the outside surface.
In accordance with the invention the lower part advantageously has at its lower end a housing for inserting a maneuvering tool for demounting the lower part of the analog.
In accordance with another feature of the analog in accordance with the invention outside surfaces of the upper and lower parts carry means for immobilizing the parts against movement in axial translation and in rotation when they are fixed in laboratory plaster.
The immobilizing means against movement in axial translation and rotation can be fins regularly distributed over the perimeter of each external surface.
Finally, the invention also relates to a dental system comprising a laboratory analog as cited above and a pin screw or a threaded part of a pin including a part to prevent rotation in both directions adapted to cooperate, through complementary shapes, with the rotation-preventing means of the analog.
The rotation-preventing part of the pin screw can be a slot or-a hexagonal housing or a cruciform housing.
The rotation-preventing part of the pin screw can equally be a hexagonal surface at the end of the screw or on the shank of the screw between the screw head and its threaded end.
The following description explains in what the invention consists and how it can be put into effect and is given with reference to the accompanying drawings, which are provided by way of non-limiting example.